This invention relates to injection processes and apparatuses for practicing the processes in which a soft ground is solidified or water leaking ground is prevented from water leakage (hereinafter the term "solidification" being used to mean both the terms "solidification" and "prevention of water leakage") by injecting a solidifying liquid, or a hardener, thereinto, and more particularly to an injection process and an injection apparatus for practicing the injection process in which a non-alkali aqueous solution of silicic acid is employed as the solidifying liquid, and further more particularly to an injection process and an injection apparatus in which an acidic aqueous solution of silicic acid satisfying certain conditions is employed as the non-alkaline aqueous solution of silicic acid.
In the case where the gelation of water glass is utilized for such an injection process of a ground, it is required for the injection liquid to meet the following conditions:
1. In order to be applicable to the mixing, the injection, and the permeation into a ground in the injection process,
(1) the gelation time of the injection liquid should be several tens of minutes to several hours or more, PA1 (2) its viscosity should be several cp to 10 cp, PA1 (3) the pH value of the injection liquid can be precisely controlled, and PA1 (4) during the injection process or a mixing process of an injection reactant, blocks of silica should not be separated out in the injection liquid. PA1 (1) the uniaxial compression strength should be several kg/cm.sup.2 -10 kg/cm.sup.2 or higher, PA1 (2) the injection liquid should be free from a reduction in strength with time, and excellent in durability. PA1 (3) the injection liquid should be excellent in solidification in water, and PA1 (4) the injection liquid should not reduce the solidification of an injection material such as cement grout to be used in combination. PA1 (1) the injection liquid should be such that the quality of water in the injection area is not caused to exceed the predetermined alkaline or acidic limitation and the organic limitation value.
2. In order to fulfill the purpose of solidification,
3. In order to follow the purpose of environmental security, or pollution prevention;
Heretofore, in a conventional ground injection process employing water glass, a reactant is added into the water glass, so as to utilize the gelation of the water glass in the alkaline region.
However, the conventional process suffers from the following drawbacks: In order to obtain a solidification strength of several to 10 kg/cm.sup.2 or higher, the concentration of the water glass must be increased. As a result, the pH value of the injection liquid is necessarily approximately 12-11, which leads to a trouble that the underground water is made alkaline.
Furthermore, since some water glass remains unreacted in the gel, the removal of such water glass due to its melting takes place for a long period of time continuously, which results in troubles that the durability of the solidified body cannot be expected, while its strength is reduced with the lapse of time.
In general, if an acidic reactant aqueous solution is gradually added into a water glass aqueous solution while being agitated, with the water glass concentration normally employed in the injection process the gelation is obtained in a range where the pH value is of the alkaline. Furthemore even if the addition of the acidic reactant aqueous solution is further continued until the pH value becomes 7 or is of the acidic, the blend will be in solidification state, that is, it has no longer fluidity.
In the case where the gelation with the pH value being 5-8 or neutral is utilized in the injection process, this method is advantageous in that the pH value of the underground water is not varied, and no variation in strength with time is caused. However, it should be noted that the uniaxial compression strength of the solidified sand is the order of 1 to several kg/cm.sup.2, and the gelation time is limited to an extremely short period of time of from a moment to several minutes (especially in summer, the gelation time being reduced more). The gelation time may be increased to several tens of minutes by decreasing the water glass concentration; however, in this case, the strength of the solidified sand is reduced very much to approximately 1 kg/cm.sup.2 or less.
As is apparent from the above description, it is difficult for the grout utilizing the gelation in the range of from the weak acidity (around 5) to approximately neutral (up to about 8) to obtain a high solidification strength, with the blending for a relatively long gelation time.
The inventor has found the following facts as a result of a variety of studies, which leads to this invention. That is, if the water glass is added and mixed and desirably mixed by jetting into an acidic reactant aqueous solution, preferably an aqueous solution of a mineral acid such an sulfuric acid, hydrochloric acid or phosphoric acid, then during the mixing operation silicic acid in the water glass is not deposited in the form of blocks of silica, and the alkali in the water glass is removed to provide a non-alkaline solution of silicic acid.
Further, it has been found that under certain conditions, i.e., at pH of 5 or less and [H.sup.+ ]/[SiO.sub.2 ].sup.n value of 1.times.10.sup.-3 or less, the pH value of the ground water in the injected ground is scarcely changed by the injection liquid which comprises the non-alkaline solution of silicic acid. The ground water is maintained at standard pH values of 5.8 to 8.6, though the injection liquid itself is acidic. When the non-alkaline solution of silicic acid which meets the aforementioned conditions is used, it is possible to provide long enough gelation time and sufficient solidification strength, and to solve problems inherent to both water glass grout of alkaline and neutral regions.
The exact reason why the ground, which has been injected the nonalkaline silica sol, assumes acidic pH value has not been elucidated, but, it is anticipated that the pH value of the aqueous silicic solution is an apparent value when it is gelled and the gelation depends upon this pH value, and the colloidal silica in the acidic aqueous solution of silicic acid contains alkali when the solution is gelled, and after the gelation a neutralization reaction takes place between said alkali and the acid present in the structure of the gel.
Experiments have shown that when the non-alkaline aqueous solution of silicic acid, which meets the aforementioned conditions and assumes acidic, is gelled and cured in water, the pH value of the curing water is acidic at the beginning and then gradually changes to neutral. This suggests that the anticipation described above is reasonable.
Employing the non-alkaline aqueous solution of silicic acid which completely meets the aforementioned conditions, it is now possible to carry out the injection process without conventional difficulties.